Tao Li, Tong Guo, Peng Wang, Zhuo Zhi, Yungen Cao, Mengmeng Cui, Jianqin Zhang
The age-dependent dynamics of cecal caproic acid and its effects on chicken myoblasts remain poorly characterized. A total of 560 female Lueyang black-boned chickens were allocated to cage-reared (CR) or free-range (FR) systems, with seven replicate units per system and 40 birds per unit. Cecal samples were collected at 120, 150, 180, and 360 d of age. Age-dependent microbial and metabolic profiles were characterized within FR chickens using shotgun metagenomics and untargeted metabolomics, whereas caproic acid abundance was compared between CR and FR chickens. Primary chicken myoblasts were used to assess cellular responses to caproic acid. Cecal caproic acid abundance was higher in FR than in CR chickens (P < 0.05). Within FR chickens, its abundance increased at 150 d, declined at 180 d, and increased again at 360 d. These dynamics coincided with age-related differences in microbial community composition and predicted carbohydrate-processing functions. The metabolite cluster containing caproic acid was positively associated with breast muscle yield and negatively associated with lipid-related traits. Caproic acid reduced myoblast viability at 500 μmol/L after 24 and 48 h and at 100-500 μmol/L after 72 h. Treatment with 300 or 400 μmol/L for 48 h reduced EdU incorporation and PCNA and CCND1 mRNA expression and their corresponding protein abundances. It also increased the proportion of cells in G0/G1 and increased apoptosis, without detectable between-group differences in culture-medium pH. The p-AMPK/AMPK and p-p38/p38 ratios increased, whereas the p-ERK/ERK ratio decreased (P < 0.05). MYOD1 mRNA expression also increased following caproic acid treatment (P < 0.05). Together, these findings identify caproic acid as an age-responsive cecal metabolite with direct effects on myoblast proliferation and survival in vitro. They provide evidence for a potential link between cecal metabolic variation and muscle-cell responses in chickens.